Fried potatoes prepared by cutting potatoes into pieces of suitable size and frying these pieces in deep fat or oil, particularly so-called French-fried potatoes, are widely consumed as a snack food and as an accompanying food for meat, fowl, and fish courses and are greatly relished because of their unique aroma, flavor, and pleasant feel in the mouth.
This fried potato can be directly prepared from the raw potato through the process steps of washing in water, peeling, cutting, draining and frying in deep fat or oil (hereinafter referred to collectively as "oil") in any ordinary kitchen such as that in a home or in a restaurant. However, in order to simplify the cooking process, it is becoming a widespread practice to produce and market semiprocessed fried potatoes so that only a short, final deep-oil frying step need be carried out in the kitchen.
Heretofore, a typical process for producing this semiprocessed fried potato has comprised washing raw potatoes in water, peeling the same, cutting the same into pieces, immersing these pieces in an aqueous solution containing an antioxidant and a texture enhancing agent, draining off water from the pieces, pre-frying the pieces in deep oil, freezing the fried pieces, and packaging the same. In this process, the freezing is carried out for the purpose of preserving the quality of the semiprocessed product and for its preservation and stable supply throughout the year. The pre-frying in deep oil is carried out for improving the quality and efficiency of the product in use. The semiprocessed fried potato thus produced is distributed and marketed in the frozen state and preserved in freeze preservation facilities owned by the consumers until the final step of frying in deep oil.
The production and distribution of the semiprocessed products produced by the above described process, however, are accompanied by difficult problems. More specifically, the semiprocessed product produced in a frozen state requires freezing facilities respectively prior to, during, and after distribution, and the cost for procuring and maintaining these facilities is considerable. Furthermore, another problem is unintentional thawing of the once-frozen semiprocessed product caused by failures in facilities such as the freezing equipment and giving rise to a serious deterioration of the product quality.
In order to avoid these problems of distribution and preservation accompanying semiprocessed products in frozen state, the production of semiprocessed fried potato for preservation at room temperature is being considered in some quarters, but has not been reduced to practice in the present state of the art. One production process proposed for this purpose is that for so-called retort foods which, after the steps of washing in water, peeling, cutting, and treating in an aqueous solution containing a texture enhancing agent and an antioxidant of the potatoes, contemplates the steps of draining, packaging the potato pieces directly as they are into retort bags, tightly sealing the bags, and retort sterilizing the bag contents by applying pressure and heat thereto.
However, the storing and distributing at room temperature of semiprocessed fried potato produced merely by such a process are accompanied by several other problems. More specifically, when the semiprocessed potato which has been packaged in a sealed bag is sterilized by heating under pressure in the final stage, moisture is driven out from the ruptured tissues of the potato by heating, and this moisture collects in the bag because of its sealed construction. Consequently, this water soaks into the semiprocessed potato, which then becomes soggy and may even assume the state of a gruel, whereby the texture of the semiprocessed potato becomes poor. Furthermore, a large quantity of excess moisture adheres also to the surfaces of the potato pieces and causes an extremely violent spattering of oil in the final cooking step of frying in deep oil, whereby this cooking step is made difficult and unpleasant.
These problems can be avoided by sufficiently drying the potato pieces prior to packaging. However, the unique aroma and flavor of fried potato arise from the direct frying in deep oil of the raw potato, and the deliciousness of eating fried potato is enhanced also by the combination of the crisp outer surface and the resilient, mealy interior part thereof. All of these desirable characteristics of fried potato cannot be obtained by frying dried potato pieces in deep oil.
While the procedure of storage and distribution of semiprocessed fried potato in this manner can be theoretically conceived in principle, it has not been reduced to actual practice.
As a result of my research, however, I have found that the deterioration of the semiprocessed fried potato represented by the above mentioned oozing out or exudation of moisture from the potato pieces is not due solely to the heating for retort sterilization but progresses with elapse of time as a consequence of overlapping of the effects of other factors. A representative factor among these is the effect of oxygen and light on the semiprocessed fried potato pieces. I have found further that, while a large quantity of moisture has a substantial effect on the deterioration of the potato pieces as described above, this difficulty can be remarkably overcome, not only by completely removing the moisture from the potato pieces in their natural state, but also by partially lowering the moisture content.
More specifically, since the solid content and the water content within a raw potato piece exist in a state of equilibrium, this equilibrium is disrupted by a variation in an external influence such as the retort sterilization treatment, whereby oozing out of water occurs. Accordingly, by causing beforehand the water content in the potato to be somewhat lower than that for the equilibrium state, the oozing out of water due to a variation in an external influence can be prevented. I have found also that when potato pieces which are in a partially dried state, and not in a completely dried state, are fried in deep oil, the above mentioned desirable characteristics of fried potato are retained and preserved.
This desirable result may be attributed to ample heating even to the innermost part of each potato piece when the final step of frying in deep oil is carried out, whereby moisture saturation occurs with a relatively low absolute water content. In the case where raw potato pieces are fried directly in deep oil, the surplus water under the heating condition is driven out of the potato pieces.
As a result of my further study conducted on the basis of the above described findings, I have found further that when potato pieces are partially dried prior to packaging and, moreover, are then packaged with an enveloping packaging material which has a gas-impervious or gas-barrier property and lightproofness, deterioration of the semiprocessed fried potato pieces during storage and distribution at room temperature can be prevented, and, at the same time, the above mentioned desirable characteristics of fried potato can be substantially preserved until the potato pieces are finally fried and eaten.